1. Field of the Invention
The present invention relates to an optical communication system based on a communication scheme using light and, more particularly, to an optical communication system to which code division multiple access is suitably applied.
2. Related Background Art
An optical communication system based on optical code division multiple access (to be referred to as an “optical CDMA system” hereinafter) is an optical communication system which shares one optical transmission line by coded optical signals from the respective users using spreading codes, thereby performing multiple access. This optical communication system uses light as a communication medium and is used for, for example, an optical communication system based on a passive optical network scheme (to be referred to as an “optical PON system” hereinafter). Assume that an optical CDMA system is to be applied to this optical PON system. In this case, when so-called upstream communication is to be performed, for example, information to be transmitted is primarily modulated into an optical signal first by the transmitting section of a terminal station used by a user. The primarily modulated optical signal is then secondarily modulated (to be referred to as “coded” hereinafter) on the basis of an assigned spreading code. The coded optical signal is transmitted to, for example, a base station used by a communication common carrier through a transmission line.
On the base station side, the coded optical signal is secondarily demodulated (to be referred to as “decoded” hereinafter) by a decoder corresponding to the spreading code. The succeeding optical detecting section primarily demodulates the decoded optical signal and determines the transmitted information. The determination result is received as the transmitted signal.
In this manner, in the optical CDMA system, an optical signal to be transmitted is coded by using a spreading code on the terminal station side, and the received optical signal is decoded by a correlator corresponding to the spreading code on the base station side, thereby performing optical communication.